This blog explains how to resolve Azure DevOps pipeline failure when running dotnet ef migration update command.
Cannot open server 'demo-sql' requested by the login. Client with IP address 'xxx.xxx.xxx.xxx' is not allowed to access the server. To enable access, use the Windows Azure Management Portal or run sp_set_firewall_rule on the master database to create a firewall rule for this IP address or address range. It may take up to five minutes for this change to take effect.